(19)
(11)EP 3 511 122 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
29.04.2020 Bulletin 2020/18

(21)Application number: 17925531.0

(22)Date of filing:  07.11.2017
(51)International Patent Classification (IPC): 
G01B 11/00(2006.01)
B23Q 17/24(2006.01)
G01B 21/04(2006.01)
G06T 7/80(2017.01)
(86)International application number:
PCT/CN2017/109782
(87)International publication number:
WO 2019/090487 (16.05.2019 Gazette  2019/20)

(54)

MONOCULAR VISION SIX-DIMENSIONAL MEASUREMENT METHOD FOR HIGH-DYNAMIC LARGE-RANGE ARBITRARY CONTOURING ERROR OF CNC MACHINE TOOL

VERFAHREN MIT MONOKULAREM SEHEN ZUR HOCHDYNAMISCHEN UND BREITBANDIGEN SECHSDIMENSIONALEN VERMESSUNG EINES KONTURFEHLERS EINER CNC-WERKZEUGMASCHINE

PROCÉDÉ DE MESURE EN SIX DIMENSIONS PAR VISION MONOCULAIRE HAUTEMENT DYNAMIQUE ET À GAMME ÉTENDUE D'UNE ERREUR DE CONTOUR ARBITRAIRE D'UNE MACHINE -OUTIL À COMMANDE NUMÉRIQUE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(43)Date of publication of application:
17.07.2019 Bulletin 2019/29

(73)Proprietor: Dalian University of Technology
Dalian, Liaoning 116024 (CN)

(72)Inventors:
  • LIU, Wei
    Dalian Liaoning 116024 (CN)
  • JIA, Zhenyuan
    Dalian Liaoning 116024 (CN)
  • LI, Xiao
    Dalian Liaoning 116024 (CN)
  • PAN, Yi
    Dalian Liaoning 116024 (CN)
  • MA, Xin
    Dalian Liaoning 116024 (CN)
  • MA, Jianwei
    Dalian Liaoning 116024 (CN)

(74)Representative: Hanna Moore + Curley 
Garryard House 25/26 Earlsfort Terrace
Dublin 2, D02 PX51
Dublin 2, D02 PX51 (IE)


(56)References cited: : 
CN-A- 101 329 164
CN-A- 105 252 341
CN-A- 105 798 704
JP-A- 2016 040 531
CN-A- 105 043 259
CN-A- 105 798 704
CN-A- 107 971 831
US-A- 5 956 253
  
  • WEI LIU ET AL: "A three-dimensional triangular vision-based contouring error detection system and method for machine tools", PRECISION ENGINEERING, vol. 50, October 2017 (2017-10), pages 85-98, XP055622180, AMSTERDAM, NL ISSN: 0141-6359, DOI: 10.1016/j.precisioneng.2017.04.016
  • XIAO LI ET AL: "A Knowledge-Driven Approach for 3D High Temporal-Spatial Measurement of an Arbitrary Contouring Error of CNC Machine Tools Using Monocular Vision", SENSORS, vol. 19, no. 3, 12 February 2019 (2019-02-12), page 744, XP055622243, DOI: 10.3390/s19030744
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

Technical Field



[0001] The present invention belongs to the field of dynamic error detection of machine tools, and relates to a six-dimensional measurement method for high-dynamic large-range arbitrary contouring error of a CNC machine tool using a monocular vision measurement technology with short-time stroboscopic illumination and a priori standard plate.

Background



[0002] Variable-curvature parts with difficult-to-machine material such as marine propellers, screw propellers for naval vessels, turbines and engine blades are widely used in major national equipment engineering. The shapes and geometrical profile accuracy of such parts directly affect the working performance of the equipment. Compared with the traditional three-axis CNC machine tool, a multi-axis machine tool solves the problem of one-time clamping and processing of most complex variable-curvature parts by virtue of control performance at any time between a cutter and a workpiece pose angle in the processing course. To achieve high quality and high efficiency machining, the hard-to-process variable-curvature parts are processed by the multi-axis CNC machine tool with special interpolation contour under high-dynamic conditions. However, in such high-traverse speed conditions, due to the prominent CNC machine tool error caused by insufficient dynamic characteristics of the machine tool, the relative position between the cutter and a workpiece in the operation of the machine tool produces space deviation and the processing quality of the workpiece is reduced. A contouring error is an important index to evaluate the dynamic performance of CNC machine tools. Therefore, the regular evaluation of high-dynamic large-range arbitrary space contouring error (dynamic performance) of the machine tool is an important guarantee to assess the dynamic performance of the CNC machine tool and improve the processing accuracy.

[0003] The existing contouring error measurement methods of the CNC machine tool include a double ball-bar measurement method, a cross-grid encoder measurement method, a R-test measurement method, a machine vision, etc. Chen jianxiong of Fuzhou University proposed detection and identification method for four position independent errors and six volumetric errors of a rotary axis in "Geometric error measurement and identification for rotary table of multi-axis machine tool using double ball bar" published in "International Journal of Machine Tools & Manufacture" on Volume 77, Issue 77. A two-step method is used in their research. According to the error identification model and the data measured by the double ball-bar, four position independent errors and six volumetric errors are separated using the identification algorithm. Although the double ball-bar equipment has high flexibility, this one-dimensional measurement equipment can only measure contouring error of a plane circle, while for contouring error of arbitrary path, it is unavailable. Furthermore, limited to the mechanical structure of the measuring rod, the double ball-bar is very difficult to measure the contouring error of a small-radius circle that can better reflect the dynamic performance of machine tools. Swiss scholars B. Bringmann et al. proposed a comprehensive method of using the spatial contour deviation measured by R-test to assist in identifying the errors both in a linear axis and a rotary axis in "A method for direct evaluation of the dynamic 3D path accuracy of NC machine tools" published in "CIRP Annals-Manufacturing Technology" on Volume 58, Issue 1. Based on the proposed identification method, the motion deviation of the machine tool can be reduced by setting acceleration and jerk parameters. R-test has high measurement accuracy, but also small measurement range. Unidirectional measurement ranges of X, Y and Z are less than 12 mm, and linkage errors of irrelevant axes may be introduced during measurement. Soichi Ibaraki et al. of Kyoto University proposed an error measurement and identification method for machine tool installation and servo systems based on cross-grid encoder in "Diagnosis and compensation of motion errors in NC machine tools by arbitrary shape contouring error measurement" published in "Laser Metrology & Machine Performance V". The servo system is compensated with feedback signals of numerical control position to improve the contour interpolation accuracy of the machine tool. However, the equipment is cumbersome to operate and unable to detect motion error of a rotary axis.

[0004] A patent for invention CN 105798704 A "Monocular vision based method for measuring plane contouring error of machine tools" applied by Liu Wei, Yan Hongyue et al. has invented a monocular vision method for contouring error detection of a CNC machine tool. The patent for invention enhances measurement efficiency, reduces cost and realizes two-dimensional measurement of the plane interpolation contouring error of the CNC machine tool. However, with this method, shooting frame frequency of the camera is difficult to be improved due to the limited camera bandwidth, resulting the blurring effect of markers in the image taken at high traverse speed of and the final vision solving accuracy of the contouring error. Besides, this two-dimensional measurement method cannot realize the three-dimensional computation of the contouring error of CNC machine tools.

Summary



[0005] The technical problem to be solved by the present invention is to overcome the defects in the prior art. For the problem that the existing single measurement method cannot realize the six-dimensional measurement of high-dynamic and large-range arbitrary contouring error of a CNC machine tool, the present invention, which is defined in claim 1, invents a monocular vision six-dimensional method for measuring high-dynamic large-range arbitrary contouring error of a CNC machine tool. A measurement fixture and a measurement system are designed. In light of the principle of error distribution, a small field of view is selected to enhance the measurement accuracy of the visible coded primitives; in combination with priori knowledge, the monocular vision pose algorithm is used to promote vision measurable dimension and range of interpolation contouring errors of machines; the whole machine tool motion contour is represented by a selected reference primitive; then, six-dimensional information (X, Y, Z, pitch, roll and yaw) of the interpolated contour represented by the reference primitive in machine tool coordinate system is obtained through datum transformation; the method is used to traverse each shot frame image to obtain the final actual six-dimensional motion contour of the machine tool; and a six-dimensional contouring error generated by the CNC machine tool interpolation is computed by comparing the measured contour with the nominal one. The measurement system of the method has low cost and simple operation.

[0006] The present invention adopts the following technical solution: A monocular vision six-dimensional measurement method for high-dynamic large-range arbitrary contouring error of a CNC machine tool is characterized in that the method designs a measurement fixture and a measuring system, and in combination with priori knowledge, the monocular vision pose algorithm is used to promote vision measurable dimension and range of interpolation contouring errors of machines; the whole machine tool motion contour is represented by a selected reference primitive; a small field of view is used to enhance the measurement accuracy of the visible coded primitives; then, six-dimensional information (X, Y, Z, pitch, roll and yaw) of the machine tool interpolation contour represented by the reference primitive in machine tool coordinate system is obtained through datum transformation; the method is used to traverse each shot frame image to obtain the final actual six-dimensional motion contour of the machine tool; a six-dimensional contouring error generated by the CNC machine tool interpolation is computed by comparing the measured contour with the nominal one; specific steps of the method are as follows:

first step: installing the measurement fixture and the measurement system
the measurement fixture is composed of a base 10, a high-brightness short-time light-emitting unit 9, a priori standard plate 7 and coded primitives 8; the priori standard plate 7 is made of transparent base material, and the coded primitives 8 with unique code values and matrice distribution are coated on the priori standard plate 7; when the measurement fixture is installed, the high-brightness short-time light-emitting unit 9 is fixed to grooves on both sides of the base 10; the priori standard plate 7 is supported on the base 10; the priori standard plate 7 is pressed by two pressing plates 6; four pressing plate locking bolts 5 are used to press and fix the priori standard plate 7 through the pressing plates 6;
the measurement system comprises a camera 1, a camera clamp 2 and the measurement fixture; the camera 1 is fixed to the camera clamp 2; the camera clamp 2 is installed above the measurement fixture to collect sequential images in the motion process of the measurement fixture; the assembled measurement fixture is put on an optical three-coordinate device platform; an optical three-coordinate device calibrates a space geometry relation among the coded primitives 8 under a global coordinate system of the priori standard plate; when the measurement system is arranged, the calibrated measurement fixture is fastened to a rotary table 3 of the CNC machine tool 4 through a pressing bolt 11 and a pressing nut 12;

second step: establishing the global coordinate system of the priori standard plate
the global coordinate system OGXGYGZG14 of the priori standard plate is established on the measurement fixture; an origin is established on the center of the coded primitive 8 in the first row and the first column, and is defined as OG; the direction of the XG coordinate axis is that the origin OG downwards points to the center point of the coded primitive 8 in the first column and the last row on the array; the direction of the YG coordinate axis is that the OG points towards the right to the center point of the coded primitive 8 in the first row and the last column on the array; the ZG coordinate axis is determined by a right-handed rule; the optical three-coordinate device is used to calibrate the space geometry relation among the coded primitives 8 under the global coordinate system OGXGYGZG14 of the priori standard plate to obtain three-dimensional coordinates of the coded primitives 8 under the global coordinate system OGXGYGZG 14 of the priori standard plate; the coded primitives 8 on the priori standard plate 7 carry motion information of the CNC machine tool 4; the spatial position relationship among the coded primitives 8 is calibrated through a high-accuracy device; on the premise of ensuring calibration accuracy, the size of the priori standard plate 7 can be made as large as possible to satisfy large-scale measurement demands of the contouring error;

third step: camera calibration
a camera imaging model expresses a one-to-one mapping relationship between a camera coordinate system and a world coordinate system; the camera imaging model with distortion parameters is:

where (Xw,Yw,Zw) is a three-dimensional coordinate of the center point of the coded primitive 8 under the world coordinate system; K is an intrinsic matrix of the camera 1; T is an extrinsic matrix of the camera 1; (u,v) is a two-dimensional coordinate of the center point of the coded primitive 8 in an image plane; (u0,v0) is coordinate of the principal point; (Cx,Cy) is an equivalent focal length in transverse and longitudinal direction;

and

are respectively rotation and translation transformation matrixes between the camera coordinate system and the world coordinate system; (δx,δy) is a distortion of an image point in the directions of x and y caused by an imperfect optical system; checker calibration board is placed in multiple positions in the field of view 21 of the camera 1 and the images is acquired; distortion parameters as well as the intrinsic and extrinsic matrixes of the camera 1 are calibrated through a calibration algorithm proposed by Zhang Zhengyou;

fourth step: high-definition no-fuzzy image collection and processing for high-dynamic and large-range interpolation contour of CNC machine tool
on the basis of completing the installation and arrangement of the measurement fixture, images of the contour interpolated by the CNC machine tool 4 are collected; because requirements for the measurement accuracy of the contouring error are high, the required field of view 21 for shooting is small; firstly, the parameters of the camera 1 are adjusted so that the camera 1 is under the optimal shooting field of view and frame frequency; subsequently, the camera 1 and the high-brightness short-time light-emitting unit 9 are synchronously triggered; light-emitting time and light-emitting intensity of the high-brightness short-time light-emitting unit 9 are set to ensure that the high-brightness short-time light-emitting unit 9 penetrates through the base of the priori standard plate 7 within the exposing time of the camera 1 and supplements light for the coded primitives 8; high-traverse speed machine tool speed which can reflect dynamic performance of the machine tool is selected; each motion axis of the CNC machine tool 4 is driven to interpolate the contour in accordance with the program instructions; in the process of image collection of the machine tool movement, the camera 1 is fixed and the machine tool moves; clear and no-fuzzy sequential images of the coded primitives 8 are collected under the assistance of the high-brightness short-time light-emitting unit 9;
after the images are collected, the code values represented by each coded primitive 8 on the images are recognized, then the two-dimensional pixel coordinates of the center point of each coded primitive 8 which is decoded is positioned through a gray centroid method; the center of coded primitives is positioned by an extraction algorithm of the gray centroid method, with a computation expression as follows:

where (i,j) represents the pixel point in image plane; m and n are the number of pixels included in the image in the transverse direction and the longitudinal direction; (x,y) is a center-of-mass coordinate of the image; f(i,j) is a gray value at the pixel coordinate (i,j);

fifth step: six-dimensional computation for high-dynamic and large-range arbitrary contouring error of CNC machine tool
in the method, a small field of view 21 is used to enhance the measurement accuracy of the coded primitives 8 in the field of view ; in combination with priori knowledge, the monocular vision pose algorithm is used to promote vision measurable dimension and range of interpolation contouring errors of machines; the whole machine tool motion contour is represented by a selected reference primitive; the position of the reference primitive in an invisible region of the field of view 21 is computed by the pixel coordinates of the primitives in visible region in combination with high-accuracy priori constraints; the motion contour represented by the reference primitive in machine tool coordinate system is obtained through datum transformation by traversing all the images; a six-dimensional contouring error generated by the interpolation of the CNC machine tool 4 is computed by comparing the measured contour with the nominal one; six-dimensional computation steps for high-dynamic and large-range arbitrary contouring error of CNC machine tool are specifically as follows:

the field of view 21 of the camera 1 is N×N (unit: mm); the external dimension of the priori standard plate 7 is M×M (unit: mm); N is much smaller than M; besides the above global coordinate system OGXGYGZG14 of the priori standard plate, involved coordinate systems also comprise a camera coordinate system OCXCYCZC13, a machine tool coordinate system OMXMYMZM15 and a local coordinate system OLiXLiYLiZLi22 of the priori standard plate; the origin of the camera coordinate system OCXCYCZC13 is established on an optical center OC; when the CNC machine tool 4 does not move, four coded primitives





and

19 arranged in a rectangle in the field of view are selected in the first frame image; the coded primitive

is selected as the reference primitive; the motion contour of the CNC machine tool 4 synthesized by the interpolation motion axis of each axis is represented by the coded primitive

the coordinate in the global coordinate system OGXGYGZG14 of the priori standard plate is

the machine tool coordinate system OMXMYMZM15 is established by taking

as an origin; the direction of each coordinate axis of the machine tool coordinate system OMXMYMZM15 is consistent with the direction of each motion axis of the CNC machine tool 4; the machine tool is controlled to drive the measurement fixture to respectively move along the X axis direction of the machine tool to multiple positions; the three-dimensional coordinate (x,y,z) of

relative to the camera coordinate system OCXCYCZC13 in each position is computed using a monocular vision pose solving algorithm; on this basis, a vector in the X axis direction is fitted; the Y axis of the machine tool coordinate system OMXMYMZM15 is determined in accordance with the same rule; the Z axis of the machine tool coordinate system OMXMYMZM15 is determined by the right-handed rule; X axis and Y axis are established in accordance with the following formula:

where

is the three-dimensional coordinates of the coded primitive

in the camera coordinate system OCXCYCZC13 in the first frame image; (x',y',z') is the three-dimensional coordinates of point

relative to the camera coordinate system OCXCYCZC13 in each position computed using the monocular vision pose solving algorithm by the measurement fixture that moves along the X axis direction of the machine tool to multiple positions; (mx,nx,px) is a vector in the X axis direction of the machine tool coordinate system OMXMYMZM15; (my,ny,py) is a vector in the Y axis direction of the machine tool coordinate system OMXMYMZM15; (CX, CY, CZ) is a three-dimensional coordinates of a point in the camera coordinate system OCXCYCZC13; (MX, MY, MZ) is a three-dimensional coordinates of a point in the machine tool coordinate system OMXMYMZM15;

is a transformation matrix between the camera coordinate system OCXCYCZC13 and the machine tool coordinate system OMXMYMZM15;

during measurement, the priori standard plate 7 continuously makes interpolation motion along with the machine tool, and the coded primitives 8 thereon are continuously imaged on the camera 1; in the motion process of the CNC machine tool 4, the camera 1 collects G frame images totally; four coded primitives 8 that appears in the field of view in the ith frame image and arranged in a rectangle are





and

the coordinates of the centers of the four coded primitives 8 in the global coordinate system OGXGYGZG14 of the priori standard plate are





and

corresponding two-dimensional pixel coordinates on the image plane are





and

a local coordinate system

(i=1,2···G) of the priori standard plate under the ith frame is established; the coordinate system takes

as a coordinate origin; XLi and YLi coordinate axis directions are respectively parallel to XG and YG directions of the global coordinate system OGXGYGZG14 of the priori standard plate; ZLi coordinate axis is determined by the right-handed rule; three-dimensional coordinates of the centers of the selected four coded primitives 8 in the local coordinate system OLiXLiYLiZLi22 of the priori standard plate are:

where Ti is a transformation matrix between the global coordinate system OGXGYGZG14 of the priori standard plate of the ith frame image and the local coordinate system OLiXLiYLiZLi22 of the priori standard plate; the ith frame image i=1,2···G is computed as follows:

where Xi is a distance from the optical center OC in the camera coordinate system OCXCYCZC13 to the

point on the priori standard plate 7 of the ith frame; Yi is a distance from the optical center OC in the camera coordinate system OCXCYCZC13 to the

point on the priori standard plate 7 of the ith frame; Zi is a distance from the optical center OC in the camera coordinate system OCXCYCZC13 to the

point on the priori standard plate 7 of the ith frame; a' is a distance between

and

in the global coordinate system OGXGYGZG14 of the priori standard plate 7 of the ith frame; b' is a distance between

and

in the global coordinate system OGXGYGZG14 of the priori standard plate of the ith frame; c' is a distance between

and

in the global coordinate system OGXGYGZG14 of the priori standard plate of the ith frame; α is an angle

between straight lines

and

β is an angle

between straight lines

and

γ is an angle

between straight lines

and







k=2cosα, q=2cosβ, r=2cosγ, c'2=vZi2, a'2=ac'2=avZi2, b'2=bc'2=bvZ2, Xi=xZi, Yi=bZi,



and

are set as three spatial points in the ith frame that are not coplanar and whose position relation is known, and k2+q2+r2-kqr-1≠0 is satisfied; equation (5) may be rewritten as formula (6);

the degenerate solution of the formula (6) is eliminated through an optimization algorithm to obtain four acceptable zero solutions;

is used as a priori constraint to obtain unique solutions of Xi, Yi and Zi; then three-dimensional coordinates



and

of



and

points on the priori standard plate 7 of the ith frame under the camera coordinate system OCXCYCZC13 are expressed as the following formula:

on the basis of the known

and

a Kabsch algorithm is used for solving a rotation matrix

and a translation matrix

of the local coordinate system OLiXLiYLiZLi22 of the priori standard plate of the ith frame relative to the camera coordinate system OCXCYCZC13;

is the three-dimensional coordinates

of the origin

of the local coordinate system OLiXLiYLiZLi22 of the priori standard plate of the ith frame in the camera coordinate system OCXCYCZC13; a pitch angle

a roll angle

and a yaw angle

between two coordinate systems are computed through

separation; the three-dimensional coordinates (CXi,CYi,CZi); (CXi,CYi,CZi)T =

of the reference primitive

in the camera coordinate system OCXCYCZC13 of the ith frame is computed according to a known spatial constraint among the coded primitives 8 of the priori standard plate 7;

the measured contouring error is represented in the machine tool coordinate system OMXMYMZM15, and the contour measured by the camera 1 needs to be subjected to coordinate transformation to correctly compute the machine tool contouring error; a pose transformation formula of the machine tool coordinate system OMXMYMZM15 and the local coordinate system OLiXLiYLiZLi22 of the priori standard plate is:

where Mi is a transformation matrix between the local coordinate system OLiXLiYLiZLi22 of the priori standard plate under the ith frame image and the machine tool coordinate system OMXMYMZM15; a pitch angle θi, a roll angle Φi and a yaw angle ψi of the ith frame standard plate relative to the machine tool coordinate system OMXMYMZM15 are separated from Mi; all image sequences are traversed to obtain a six-degree-of-freedom contour Lr of the whole machine tool represented by the reference primitive, where Lr(MXi, MYi, MZi, θi, Φi, ψi) and i=1,2···G; a six-degree-of-freedom contouring error E generated by interpolation of the CNC machine tool 4 is computed by comparing the actual six-degree-of-freedom contour Lr with the nominal contour Lm:



[0007] Compared with the existing vision method, the present invention has the beneficial effects of enhancing vision measurable interpolation speed of the CNC machine tool, breaking through measurable speed limit of the machine tool and extending vision measurable interpolation traverse speed range of the CNC machine tool. Furthermore, to ensure measurement accuracy of the contouring error, the field of view is less. The present invention uses a vision pose algorithm to realize six-dimensional measurement for large-range arbitrary contouring error of the CNC machine tool under small field of view in combination with priori spatial constraints among the coded primitives on the large-size standard plate, and extends measurable motion range and measurement dimension of the vision system. In the measurement process, only a single camera, a specially-made measurement fixture and a specially-made measurement system are adopted, so that operation simplicity is enhanced while the cost is reduced.

Description of Drawings



[0008] 

Fig. 1 is a diagram of a six-dimensional measurement system for high-dynamic large-range arbitrary contouring error of a CNC machine tool. In the figure, 1-camera; 2-camera clamp; 3-rotary table; and 4-CNC machine tool.

Fig. 2 is an exploded view of a measurement fixture. In the figure, 5-pressing plate locking bolt; 6-pressing plate; 7-priori standard plate; 8-coded primitive; 9-high-brightness short-time light-emitting unit; 10-base; 11-pressing bolt; and 12-pressing nut.

Fig. 3 is an arrangement diagram of a measurement system and each coordinate system when a machine tool does not move. In the figure, 13-camera coordinate system OCXCYCZC; 14-global coordinate system OGXGYGZG of priori standard plate; 15-machine tool coordinate system OMXMYMZM; 16-coded primitive

17-coded primitive

18-coded primitive

19-coded primitive

20-local coordinate system OL1XL1YL1ZL1 of priori standard plate of first frame; and 21- field of view of camera.

Fig. 4 shows an identification and positioning result of a coded primitive of the 300th frame image.

Fig. 5 shows the X component of the machine tool interpolated contouring error solved by the vision method.

Fig. 6 shows the Y component of the machine tool interpolated contouring error solved by the vision method.

Fig. 7 shows the Z component of the machine tool interpolated contouring error solved by the vision method.

Fig. 8 shows the pitch component θi of the machine tool interpolated contouring error solved by the vision method.

Fig. 9 shows the roll component Φi of the machine tool interpolated contouring error solved by the vision method.

Fig. 10 shows the yaw component ψi of the machine tool interpolated contouring error solved by the vision method.


Detailed Description



[0009] Specific embodiments of the present invention are described below in detail in combination with the technical solution and accompanying drawings.

[0010] To reflect the arbitrariness of the path, a plane interpolation equiangular spiral contour of a CNC machine tool is taken as a research object, and the six-dimensional contouring error is solved using the vision detection method of the present invention. The equation of the equiangular spiral contour to be measured is r=0.189e0.221θ, θ=[0,7.3π]. Six-dimensional solving steps of the equiangular spiral contouring error are specifically as follows:

First step: designing and installing a measurement fixture and a measurement system



[0011] As shown in Fig. 1, a measurement object is a self-designed CNC machine tool 4. The strokes of the CNC machine tool 4 in X direction and Y direction are respectively 800mm and 900mm. To reflect the dynamic performance of the machine tool, the interpolation speed of the machine tool is selected as 3m/min. The measurement system comprises a camera 1, a camera clamp 2 and the measurement fixture. In the embodiment, the selected camera 1 has a frame frequency of 60fps, a resolution of 3300× 3300 pixels and an exposing time of 5000 µs. The camera clamp 2 can realize six-pose adjustment of the camera 1. The measurement fixture is composed of a base 10, a high-brightness short-time light-emitting unit 9, a priori standard plate 7 and coded primitives 8. The measurement fixture is installed on a rotary table of the CNC machine tool.

[0012] Fig. 2 is an exploded view of the measurement fixture. The priori standard plate 7 is made of transparent glass material having an external dimension of 250mm × 250mm, and 196 coded primitives 8 distributed in a matrix are photoetched on the priori standard plate 7. Each coded primitive 8 is sampled and valued from [65, 637], and has unique code value. The center distance between adjacent coded primitives 8 is 16mm.

[0013] Each unit is assembled in accordance with the exploded view of the measurement fixture shown in Fig. 2. The specific assembling sequence is: the high-brightness short-time light-emitting unit 9 is inserted into grooves on both sides of the base 10; the priori standard plate 7 is put on the base 10; the priori standard plate 7 is pressed by two pressing plates 6; and four pressing plate locking bolts 5 are used to press and fix the priori standard plate 7 through the pressing plates 6.

[0014] The assembled measurement fixture is put on an optical three-coordinate device platform; and a global coordinate system OGXGYGZG14 of the priori standard plate is established, as shown in Fig. 3. The optical three-coordinate device is used to calibrate the space geometry relation among the coded primitives 8 in the global coordinate system OGXGYGZG14 of the priori standard plate; the measurement and detection accuracy of an optical three-coordinate space is 0.5 µm; and three-dimensional coordinates of the coded primitives 8 in the global coordinate system OGXGYGZG14 of the priori standard plate are obtained.

[0015] The calibrated measurement fixture is fastened to a rotary table of the CNC machine tool 4 through a pressing bolt 11 and a pressing nut 12. In installation, the camera 1 is fixed to the camera clamp 2; and six-dimensional pose parameters of the camera 1 are adjusted to ensure that the camera clamp 2 is positioned above the measurement fixture to collect sequential images of the coded primitives 8 in the motion process of the measurement fixture. Imaging parameters of the camera 1 are adjusted. The field of view 21 of the camera 1 is 40mm×40mm, and the measurement distance is about 337mm.

Second step: camera calibration



[0016] High-accuracy two-dimensional checker calibration board are placed in 16 positions in the field of view 21 of the camera 1; and the camera 1 is triggered in each position to shoot the images of the calibration boards. Intrinsic and extrinsic parameters and distortion parameters of the camera 1 are calibrated through a calibration algorithm proposed by Zhang Zhengyou in combination with the formula (1). The equivalent focal length of the calibrated transverse direction and longitudinal direction is: (αx, αy)=(14959.25, 14959.68); the principal point of the image is (u0, v0)=(2557.11, 2599.79); five distortion factors to be solved for expressing distortion are (0.10328, -0.23054, 0.00045, 0.00012, 0).

Third step: high-definition no-fuzzy image collection and processing for high-dynamic and large-range interpolation contour of CNC machine tool



[0017] Image sequence of the plane equiangular spiral contour interpolated by the CNC machine tool 4 is collected and processed. The camera 1 and the high-brightness short-time light-emitting unit 9 are synchronously triggered, then the X axis and Y axis of the CNC machine tool 4 are driven to interpolate the contour; and the light-emitting time of the high-brightness short-time light-emitting unit 9 in each frame is set as 700 µs to ensure high contrast of the collected sequential images. After the images are collected, the code value of the coded primitive 8 in each frame image is identified, and the pixel coordinates of the center point of each coded primitive 8 is positioned through a gray centroid method in combination with the formula (2). Fig. 4 shows a processing result of image identification and positioning of a coded primitive 8.

Fourth step: six-dimensional computation for high-dynamic and large-range arbitrary contouring error of CNC machine tool



[0018] The field of view 21 of the adopted camera 1 is 40mm × 40mm; the external dimension of the priori standard plate 7 is 250mm × 250mm; the scope of the measured equiangular spiral contour is [90mm, 70mm]; and the field of view 21 of the camera 1 is less than the range of the contour interpolated by the machine tool. The whole machine tool motion contour is represented by a coded primitive 8 selected on the first frame image. The position of this primitive in an invisible region is estimated through a space geometry relation among the coded primitives 8 on the large-size priori standard plate 7, so as to realize large-range contouring error measurement of the CNC machine tool 4. Specific steps are as follows:

Step 1 The camera coordinate system OCXCYCZC13 is established with reference to Fig. 3; the coded primitive

with a code value of 235 in the sixth row and the ninth column on the priori standard plate is selected from the first image frame as a reference primitive; the coded primitive 8 with a code value of 237 in the sixth row and the tenth column is selected as a second coded primitive

the coded primitive 8 with a code value of 285 in the seventh row and the tenth column is selected as a third coded primitive

the coded primitive 8 with a code value of 283 in the seventh row and the ninth column is selected as a fourth coded primitive

the coded primitive

with a code value of 235 is selected as an origin, so as to establish a local coordinate system OL1XL1YL1ZL120 and a machine tool coordinate system OMXMYMZM15 of the first frame priori standard plate; and a transformational relation between the camera coordinate system OCXCYCZC13 and the machine tool coordinate system OMXMYMZM15 is established according to the formula (3), as follows:

Step 2 The camera 1 shoots 500 images in the whole contour measurement process; the embodiment analyzes and shoots the 300th frame image; the coded primitive on the ninth row and the eighth column is selected as a first coded primitive

selected by the 300th frame; the coded primitive on the ninth row and the ninth column is selected as a second coded primitive

of the 300th frame; the coded primitive in the tenth row and the ninth column is selected as a third coded primitive

of the 300th frame; and the coded primitive in the tenth row and the eighth column is selected as a fourth coded primitive

of the 300th frame. The local coordinate system OL300-XL300YL300ZL30021 of the priori standard plate under the 300th frame is established. The coordinates of four points in the global coordinate system OG-XGYGZG14 of the priori standard plate are respectively (112.0010, 128.0024, 0.0110), (127.9990, 128.0021, 0.0111), (128.0012, 144.0037, 0.0120) and (112.0008, 144.0057, 0.0146). The coordinates of four points in the local coordinate system OL300-XL300YL300ZL30021 of the priori standard plate are computed through the formula (5): (0, 0, 0), (15.9980, -0.0030, -0.0010), (16.0003, 16.0013, 0.0010) and (-0.0002, 16.0033, 0.0036). The pixel coordinates on the image plane of the camera 1 are (1452.39, 1071.15), (2497.23, 683.88), (2884.75, 1729.45) and (1839.66, 2116.14). CX300, CY300, CZ300, pitch angle

roll angle

and yaw angle

of the priori standard plate 7 of the 300th frame image under the camera coordinate system OCXCYCZC13 are computed according to formulas 5-7. Computation results are: (-10.9098mm, - 3.08975mm, 337.696, -179.931°, 0.19436°, -0.00356046°).

Step 3 The six-dimensional information of MX300, MY300, MZ300, pitch angle θ300, roll angle Φ300 and yaw angle ψ300 of the 300th frame image in the machine tool coordinate system OM-XMYMZM15 is computed as (12.3424, 2.3471, - 0.051,, -0.211°, 0.056°, -0.002°).

Step 4 Each shot frame image is traversed in accordance with the above method to obtain the final interpolation contour in the machine tool coordinate system OMXMYMZM15 represented by the coded primitive 8 with a code value of 235; and the six-degree-of-freedom contouring error of the path interpolated by the CNC machine tool 4 is solved by comparing the actual six-degree-of-freedom contour Lr with the nominal contour Lm. Fig. 5, Fig. 6 and Fig. 7 respectively show X, Y and Z components of the machine tool interpolated contouring error solved by the vision method. Fig. 8, Fig. 9 and Fig. 10 respectively show pith, roll and yaw components of the machine tool interpolated contouring error solved by the vision method. It can be clearly seen from the figures that, the method can be used to conveniently solve a contouring error of the path interpolated by the machine tool.



[0019] The method uses a monocular vision pose algorithm to realize six-dimensional measurement for large-range arbitrary contouring error of the CNC machine tool under small field of view in combination with priori spatial constraints among the coded primitives on the large-size standard plate, and extends measurable motion range and measurement dimension of the vision system. The measurement system and method of the present invention have low cost and simple operation.


Claims

1. A monocular vision six-dimensional measurement method for high-dynamic large-range arbitrary contouring error of CNC machine tool, wherein the method uses a measurement fixture and a measuring system which are specially designed, and in combination with priori knowledge, the monocular vision pose algorithm is used to promote vision measurable dimension and range of interpolation contouring errors of machines; the whole machine tool motion contour is represented by a selected reference primitive; a small field of view is used to enhance the measurement accuracy of the visible coded primitives; then, six-dimensional information of X, Y, Z, pitch, roll and yaw of the machine tool interpolation contour represented by the reference primitive in machine tool coordinate system is obtained through datum transformation; the method is used to traverse each shot frame image to obtain the final actual six-dimensional motion contour of the machine tool; a six-dimensional contouring error generated by the CNC machine tool interpolation is computed by comparing the measured contour with the nominal one; wherein the method comprises the following steps:

first step: installing the measurement fixture and the measurement system which are specially made, wherein the measurement fixture specially made is composed of a base (10), a high-brightness short-time light-emitting unit (9), a priori standard plate (7) and coded primitives (8); the priori standard plate (7) is made of transparent base material, and the coded primitives (8) with unique code values and matrice distribution are coated on the priori standard plate (7); when the measurement fixture is installed, the high-brightness short-time light-emitting unit (9) is inserted into grooves on both sides of the base (10); the priori standard plate (7) is supported on the base (10); the priori standard plate (7) is pressed by two pressing plates (6); four pressing plate locking bolts (5) are used to press and fix the priori standard plate (7) through the pressing plates (6);
the measurement system comprises a camera (1), a camera clamp (2) and the measurement fixture; the camera (1) is fixed to the camera clamp (2); the camera clamp (2) is installed above the measurement fixture to collect sequential images in the motion process of the measurement fixture; the assembled measurement fixture is put on an optical three-coordinate device platform; an optical three-coordinate device calibrates a space geometry relation among the coded primitives (8) under a global coordinate system of the priori standard plate; when the measurement system is arranged, the calibrated measurement fixture is fastened to a rotary table (3) of the CNC machine tool (4) through a pressing bolt (11) and a pressing nut (12);

second step: establishing the global coordinate system of the priori standard plate, wherein the global coordinate system OGXGYGZG (14) of the priori standard plate is established on the measurement fixture; an origin is established on the center of the coded primitive (8) in the first row and the first column, and is defined as OG; the direction of the XG coordinate axis is that the origin OG downwards points to the center point of the coded primitive (8) in the first column and the last row on the array; the direction of the YG coordinate axis is that the OG points towards the right to the center point of the coded primitive (8) in the first row and the last column on the array; the ZG coordinate axis is determined by a right-handed rule; the optical three-coordinate device is used to calibrate the space geometry relation among the coded primitives (8) under the global coordinate system OGXGYGZG (14) of the priori standard plate to obtain three-dimensional coordinates of the coded primitives (8) under the global coordinate system OGXGYGZG (14) of the priori standard plate; the coded primitives (8) on the priori standard plate (7) carry motion information of the CNC machine tool (4); the spatial position relationship among the coded primitives (8) is calibrated through a high-accuracy device; on the premise of ensuring calibration accuracy, the size of the priori standard plate (7) can be made as large as possible to satisfy large-scale measurement demands of the contouring error;

third step: camera calibration, wherein a camera imaging model expresses a one-to-one mapping relationship between a camera coordinate system and a world coordinate system; the camera imaging model with distortion parameters is:

where (Xw,Yw,Zw) is a three-dimensional coordinate of the center point of the coded primitive (8) under the world coordinate system; K is an intrinsic matrix of the camera (1); T is an extrinsic matrix of the camera (1); (u,v) is a two-dimensional coordinate of the center point of the coded primitive (8) in an image plane; (u0,v0) is coordinate of the principal point; (Cx,Cy) is an equivalent focal length in transverse and longitudinal direction;

and

are respectively rotation and translation transformation matrixes between the camera coordinate system and the world coordinate system; (δx,δy) is a distortion of an image point in the directions of x and y caused by an imperfect optical system; a checker calibration board is placed in multiple positions in the field of view (21) of the camera (1) and the images are acquired; distortion parameters as well as the intrinsic and extrinsic matrixes of the camera (1) are calibrated through a calibration algorithm;

fourth step: high-definition no-fuzzy image collection and processing for high-dynamic and large-range interpolation contour of CNC machine tool, wherein,

on the basis of completing the installation and arrangement of the measurement fixture, images of the contour interpolated by the CNC machine tool (4) are collected; because requirements for the measurement accuracy of the contouring error are high, the required field of view (21) for shooting is small; firstly, the parameters of the camera (1) are adjusted so that the camera (1) is under the optimal shooting field of view and frame frequency; subsequently, the camera (1) and the high-brightness short-time light-emitting unit (9) are synchronously triggered; light-emitting time and light-emitting intensity of the high-brightness short-time light-emitting unit (9) are set to ensure that the high-brightness short-time light-emitting unit (9) penetrates through the base of the priori standard plate (7) within the exposing time of the camera (1) and supplements light for the coded primitives (8); high-traverse speed machine tool speed which can reflect dynamic performance of the machine tool is selected; each motion axis of the CNC machine tool (4) is driven to interpolate the contour in accordance with the program instructions; in the process of image collection of the machine tool movement, the camera (1) is fixed and the machine tool moves; clear and no-fuzzy sequential images of the coded primitives (8) are collected under the assistance of the high-brightness short-time light-emitting unit (9);
after the images are collected, the code values represented by each coded primitive (8) on the images are recognized, then the two-dimensional pixel coordinates of the center point of each decoded coded primitive (8) is positioned through a gray centroid method; the center of coded primitives is positioned by an extraction algorithm of the gray centroid method, with a computation expression as follows:

where (i,j) represents the pixel point in image plane; m and n are the number of pixels included in the image in the transverse direction and the longitudinal direction; (x,y) is a center-of-mass coordinate of the image; f(i,j) is a gray value at the pixel coordinate (i,j);

fifth step: six-dimensional computation for high-dynamic and large-range arbitrary contouring error of CNC machine tool, wherein, in the method, a small field of view (21) is used to enhance the measurement accuracy of the coded primitives (8) in the field of view; in combination with priori knowledge, the monocular vision pose algorithm is used to promote vision measurable dimension and range of interpolation contouring errors of machines; the whole machine tool motion contour is represented by a selected reference primitive; the position of the reference primitive in an invisible region of the field of view (21) is computed by the pixel coordinates of the primitives in visible region in combination with high-accuracy priori constraints; the motion contour represented by the reference primitive in the machine tool coordinate system is obtained through datum transformation by traversing all the images; a six-dimensional contouring error generated by the interpolation of the CNC machine tool (4) is computed by comparing the measured contour with the nominal one; wherein six-dimensional computation steps for high-dynamic and large-range arbitrary contouring error of CNC machine tool are specifically as follows:

the field of view (21) of the camera (1) is N×N in units of mm; the external dimension of the priori standard plate (7) is M×M in units of mm; N is much smaller than M; besides the above global coordinate system OG-XGYGZG (14) of the priori standard plate, involved coordinate systems also comprise a camera coordinate system OC-XCYCZC (13), a machine tool coordinate system OM-XMYMZM (15) and a local coordinate system OLi-XLiYLiZLi (22) of the priori standard plate; the origin of the camera coordinate system OC-XCYCZC (13) is established on an optical center OC; when the CNC machine tool (4) does not move, four coded primitives





and

arranged in a rectangle in the field of view are selected in the first frame image; the coded primitive

is selected as a reference primitive; the motion contour of the CNC machine tool (4) synthesized by the interpolation motion axis of each axis is represented by the coded primitive

the coordinate in the global coordinate system OG-XGYGZG (14) of the priori standard plate is

the machine tool coordinate system OM-XMYMZM (15) is established by taking

as an origin; the direction of each coordinate axis of the machine tool coordinate system OM-XMYMZM (15) is consistent with the direction of each motion axis of the CNC machine tool (4); the machine tool is controlled to drive the measurement fixture to respectively move along the X axis direction of the machine tool to multiple positions; the three-dimensional coordinate (x,y,z) of

relative to the camera coordinate system OC-XCYCZC (13) in each position is computed using a monocular vision pose solving algorithm; on this basis, a vector in the X axis direction is fitted; the Y axis of the machine tool coordinate system OM-XMYMZM (15) is determined in accordance with the same rule; the Z axis of the machine tool coordinate system OM-XMYMZM (15) is determined by the right-handed rule; X axis and Y axis are established in accordance with the following formula:

where

is the three-dimensional coordinates of the coded primitive

in the camera coordinate system OCXCYCZC (13) in the first frame image; (x',y',z') is the three-dimensional coordinates of point

relative to the camera coordinate system OCXCYCZC (13) in each position computed using the monocular vision pose solving algorithm by the measurement fixture that moves along the X axis direction of the machine tool to multiple positions; (mx,nx,px) is a vector in the X axis direction of the machine tool coordinate system OMXMYMZM (15); (my,ny,py) is a vector in the Y axis direction of the machine tool coordinate system OMXMYMZM (15); (CX, CY, CZ) is a three-dimensional coordinates of a point in the camera coordinate system OCXCYCZC (13); (MX, MY, MZ) is a three-dimensional coordinates of a point in the machine tool coordinate system OMXMYMZM (15);

is a transformation matrix between the camera coordinate system OCXCYCZC (13) and the machine tool coordinate system OMXMYMZM (15);

during measurement, the priori standard plate (7) continuously makes interpolation motion along with the machine tool, and the coded primitives (8) thereon are continuously imaged on the camera (1); in the motion process of the CNC machine tool (4), the camera (1) collects G frame images totally; four coded primitives (8) that appears in the field of view in the ith frame image and arranged in a rectangle are





and

the coordinates of the centers of the four coded primitives (8) in the global coordinate system OGXGYGZG (14) of the priori standard plate are






and

corresponding two-dimensional pixel coordinates on the image plane are





and

a local coordinate system OLiXLiYLiZLi (22) of the priori standard plate under the ith frame is established, where i is an integer between 1 and G; the coordinate system takes

as a coordinate origin; XLi and YLi coordinate axis directions are respectively parallel to XG and YG directions of the global coordinate system OGXGYGZG (14) of the priori standard plate; ZLi coordinate axis is determined by the right-handed rule; three-dimensional coordinates of the centers of the selected four coded primitives (8) in the local coordinate system OLiXLiYLiZLi (22) of the priori standard plate are:

where m = 1,2,3,4 and Ti is a transformation matrix between the global coordinate system OGXGYGZG (14) of the priori standard plate of the ith frame image and the local coordinate system OLiXLiYLiZLi (22) of the priori standard plate; the ith frame image is computed according to the following equation A:

where Xi is a distance from the optical center OC in the camera coordinate system OCXCYCZC (13) to the

point on the priori standard plate (7) of the ith frame; Yi is a distance from the optical center OC in the camera coordinate system OCXCYCZC (13) to the 24 point on the priori standard plate (7) of the ith frame; Zi is a distance from the optical center OC in the camera coordinate system OCXCYCZC (13) to the

point on the priori standard plate (7) of the ith frame; a' is a distance between

and

in the global coordinate system OGXGYGZG of the priori standard plate (7) of the ith frame; b' is a distance between

and

in the global coordinate system OGXGYGZG (14) of the priori standard plate of the ith frame; c' is a distance between

and

in the global coordinate system OGXGYGZG (14) of the priori standard plate of the ith frame; α is an angle

between straight lines

and

β is an angle

between straight lines

and

γ is an angle

between straight lines

and







k=2cosα, q=2cosβ, r=2cosy, c'2=vZi2, a'2=ac'2=avZi2,

Xi=xZi, Yi=yZi,



and

are set as three spatial points in the ith frame that are not coplanar and whose position relation is known, and k2+q2+r2-kqr-1≠0 is satisfied; equation A is rewritten as formula B:

the degenerate solution of formula B is eliminated through an optimization algorithm to obtain four acceptable zero solutions;

is used as a priori constraint to obtain unique solutions of Xi, Yi and Zi; then three-dimensional coordinates



and

of



and

points on the priori standard plate (7) of the ith frame under the camera coordinate system OCXCYCZC (13) are expressed as the following formula:

where j = 1,2,4 and i = 1,2 ... G; on the basis of the known

and

a Kabsch algorithm is used for solving a rotation matrix

and a translation matrix

of the local coordinate system OLiXLiYLiZLi(22) of the priori standard plate of the ith frame relative to the camera coordinate system OC-XCYCZC (13);

is the three-dimensional coordinates

of the origin

of the local coordinate system OLiXLiYLiZLi (22) of the priori standard plate of the ith frame in the camera coordinate system OCXCYCZC (13); a pitch angle

a roll angle

and a yaw angle

between two coordinate systems are computed through

separation; the three-dimensional coordinates (CXi, CYi, CZi), with

of the reference primitive

in the camera coordinate system OCXCYCZC (13) of the ith frame is computed according to a known spatial constraint among the coded primitives (8) of the priori standard plate (7);

the measured contouring error is represented in the machine tool coordinate system OMXMYMZM(15), and the contour measured by the camera (1) needs to be subjected to coordinate transformation to correctly compute the machine tool contouring error; a pose transformation formula of the machine tool coordinate system OMXMYMZM (15) and the local coordinate system OLiXLiYLiZLi (22) of the priori standard plate is:

where Mi is a transformation matrix between the local coordinate system OLiXLi YLiZLi (22) of the priori standard plate under the ith frame image and the machine tool coordinate system OMXMYMZM (15); a pitch angle θi, a roll angle Φi and a yaw angle ψi of the ith frame standard plate relative to the machine tool coordinate system OMXMYMZM (15) are separated from Mi; all image sequences are traversed to obtain a six-degree-of-freedom contour Lr of the whole machine tool represented by the reference primitive, where Lr(MXi, MYi, MZi, θi, Φi, ψi) and i=1,2···G; a six-degree-of-freedom contouring error E generated by interpolation of the CNC machine tool (4) is computed by comparing the actual six-degree-of-freedom contour Lr with the nominal contour Lm:


 


Ansprüche

1. Sechsdimensionales Monokularsicht-Messverfahren für einen willkürlichen Konturfehler mit hoher Dynamik und großem Bereich einer CNC-Werkzeugmaschine, wobei das Verfahren eine Messvorrichtung und ein Messsystem verwendet, die speziell entworfen sind, und in Kombination mit Priori-Wissen der Monokularsicht-Pose-Algorithmus verwendet wird, um sichtmessbare Dimensions- und Interpolationsbereichskonturfehler von Maschinen zu begünstigen; die gesamte Werkzeugmaschinenbewegungskontur durch eine ausgewählte Referenzprimitive dargestellt wird; ein kleines Sichtfeld verwendet wird, um die Messgenauigkeit der sichtbaren codierten Primitiven zu verbessern; dann sechsdimensionale Information von X, Y, Z, Nick-, Roll- und Gierwinkel, der Werkzeugmaschineninterpolationskontur, die durch die Referenzprimitive in einem Werkzeugmaschinenkoordinatensystem dargestellt ist, durch Datumstransformation erhalten werden; das Verfahren dazu verwendet wird, jedes aufgenommenen Rahmenbilds zu durchlaufen, um die tatsächliche sechsdimensionale Endbewegungskontur der Werkzeugmaschine zu erhalten; ein sechsdimensionaler Konturfehler, der durch die CNC-Werkzeugmaschineninterpolation erzeugt wird, durch Vergleichen der gemessenen Kontur mit der Nennkontur berechnet wird; wobei das Verfahren die folgenden Schritte umfasst:

erster Schritt: Installieren der Messvorrichtung und des Messsystems, die speziell hergestellt sind, wobei die speziell hergestellte Messvorrichtung sich aus einer Basis (10), einer Einheit (9) zur Emission von Licht mit hoher Helligkeit für kurze Zeit, einer Priori-Standardplatte (7) und codierten Primitiven (8) zusammensetzt; die Priori-Standardplatte (7) aus einem transparenten Grundmaterial hergestellt ist und die codierten Primitiven (8) mit einzigartigen Codewerten und einer einzigartigen Matrixverteilung auf die Priori-Standardplatte (7) beschichtet sind; wenn die Messvorrichtung installiert ist, die Einheit (9) zur Emission von Licht mit hoher Helligkeit für kurze Zeit in Nuten auf beiden Seiten der Basis (10) eingesetzt wird; die Priori-Standardplatte (7) auf der Basis (10) getragen wird; die Priori-Standardplatte (7) durch zwei Pressplatten (6) gepresst wird; vier Pressplattenverriegelungsbolzen (5) dazu verwendet werden, die Priori-Standardplatte (7) durch die Pressplatten (6) zu pressen und zu befestigen;

wobei das Messsystem eine Kamera (1), eine Kameraklemme (2) und die Messvorrichtung umfasst; die Kamera (1) an der Kameraklemme (2) befestigt ist; die Kameraklemme (2) über der Messvorrichtung installiert ist, um sequentielle Bilder in dem Bewegungsvorgang der Messvorrichtung zu sammeln; die zusammengefügte Messvorrichtung auf eine optische Drei-Koordinaten-Geräteplattform gesetzt wird; ein optisches Drei-Koordinaten-Gerät eine Raumgeometriebeziehung zwischen den codierten Primitiven (8) unter einem globalen Koordinatensystem der Priori-Standardplatte kalibriert; wenn das Messsystem eingerichtet ist, die kalibrierte Messvorrichtung durch einen Pressbolzen (11) und eine Pressmutter (12) an einem Drehtisch (3) der CNC-Werkzeugmaschine (4) angebracht wird;

zweiter Schritt: Ermitteln des globalen Koordinatensystems der Priori-Standardplatte, wobei das globale Koordinatensystem OGXGYGZG (14) der Priori-Standardplatte an der Messvorrichtung ermittelt wird; ein Ausgangspunkt an der Mitte der codierten Primitive (8) in der ersten Zeile und der ersten Spalte ermittelt und als OG definiert wird; die Richtung der XG-Koordinatenachse darin besteht, dass der Ausgangspunkt OG nach unten zum Mittelpunkt der codierten Primitive (8) in der ersten Spalte und der letzten Zeile auf dem Array zeigt; die Richtung der YG-Koordinatenachse darin besteht, dass der OG nach rechts zum Mittelpunkt der codierten Primitive (8) in der ersten Zeile und der letzten Spalte auf dem Array zeigt; die ZG-Koordinatenachse durch eine Drei-Finger-Regel bestimmt wird; das optische Drei-Koordinaten-Gerät dazu verwendet wird, die Raumgeometriebeziehung zwischen den codierten Primitiven (8) unter dem globalen Koordinatensystem OGXGYGZG (14) der Priori-Standardplatte zu kalibrieren, um dreidimensionale Koordinaten der codierten Primitiven (8) unter dem globalen Koordinatensystem OGXGYGZG (14) der Priori-Standardplatte zu erhalten; die codierten Primitiven (8) auf der Priori-Standardplatte (7) Bewegungsinformationen der CNC-Werkzeugmaschine (4) tragen; die Raumpositionsbeziehung zwischen den codierten Primitiven (8) durch ein Hochgenauigkeitsgerät kalibriert wird; vorausgesetzt, dass eine Kalibriergenauigkeit sichergestellt wird, die Größe der Priori-Standardplatte (7) so groß wie möglich hergestellt werden kann, um weiträumigen Messanforderungen des Konturfehlers zu genügen;

dritter Schritt: Kamerakalibrierung, wobei ein Kamerabildgebungsmodell eine Eins-zu-Eins-Abbildungsbeziehung zwischen einem Kamerakoordinatensystem und einem Weltkoordinatensystem ausdrückt, wobei das Kamerabildgebungsmodell mit Verzerrungsparametern ist:

wobei (Xw, Yw, Zw) eine dreidimensionale Koordinate des Mittelpunkts der codierten Primitive (8) unter dem Weltkoordinatensystem ist; K eine intrinsische Matrix der Kamera (1) ist; T eine extrinsische Matrix der Kamera (1) ist; (u,v) eine zweidimensionale Koordinate des Mittelpunkts der codierten Primitive (8) in einer Bildebene ist; (u0,v0) eine Koordinate des Hauptpunkts ist; (Cx,Cy) eine äquivalente Brennweite in Quer- und Längsrichtung ist; RIc und TIc eine Drehungs- bzw. eine Übersetzungsumwandlungsmatrix zwischen dem Kamerakoordinatensystem und dem Weltkoordinatensystem sind; (δxy) eine Verzerrung eines Bildpunkts in den Richtungen von x und y ist, die von einem mangelhaften optischen System verursacht wird; ein Kalibrierschachbrett in mehreren Positionen im Sichtfeld (21) der Kamera (1) platziert wird und die Bilder bezogen werden; Verzerrungsparameter sowie die intrinsische und die extrinsische Matrix der Kamera (1) durch einen Kalibrieralgorithmus kalibriert werden;

vierter Schritt: Sammlung und Verarbeitung von Bilder mit hoher Auflösung und ohne Unschärfen für eine Interpolationskontur mit hoher Dynamik und großem Bereich einer CNC-Werkzeugmaschine, wobei

auf der Basis eines Abschließens der Installation und der Einrichtung der Messvorrichtung Bilder der Kontur, die von der CNC-Werkzeugmaschine (4) interpoliert wurde, gesammelt werden; da Anforderungen an die Messgenauigkeit des Konturfehlers hoch sind, das erforderliche Sichtfeld (21) zum Aufnehmen klein ist; erstens die Parameter der Kamera (1) justiert werden, so dass die Kamera (1) unter dem optimalen Aufnahmesichtfeld und der optimalen Bildfrequenz ist; anschließend die Kamera (1) und die Einheit (9) zur Emission von Licht mit hoher Helligkeit für kurze Zeit synchron ausgelöst werden; die Lichtemissionszeit und die Lichtemissionsintensität der Einheit (9) zur Emission von Licht mit hoher Helligkeit für kurze Zeit eingestellt werden, um sicherzustellen, dass die Einheit (9) zur Emission von Licht mit hoher Helligkeit für kurze Zeit durch die Basis der Priori-Standardplatte (7) innerhalb der Belichtungszeit der Kamera (1) hindurchdringt und Licht für die codierten Primitive (8) ergänzt; die Geschwindigkeit der Werkzeugmaschine mit hoher Verfahrgeschwindigkeit, die die dynamische Leistung der Werkzeugmaschine widerspiegeln kann, ausgewählt wird; jede Bewegungsachse der CNC-Werkzeugmaschine (4) angetrieben wird, um die Kontur gemäß den Programmanweisungen zu interpolieren; die Kamera (1) im Bildsammlungsvorgang der Werkzeugmaschinenbewegung befestigt ist und die Werkzeugmaschine sich bewegt; sequentielle klare Bilder ohne Unschärfen der codierten Primitive (8) unter der Unterstützung der Einheit (9) zur Emission von Licht mit hoher Helligkeit für kurze Zeit gesammelt werden;

nachdem die Bilder gesammelt wurden, die Codewerte, die durch jede codierte Primitive (8) auf den Bildern dargestellt werden, erkannt werden, dann die zweidimensionalen Pixelkoordinaten des Mittelpunkts jeder decodierten codierten Primitive (8) durch ein Grauer-Schwerpunkt-Verfahren positioniert werden; die Mitte von codierten Primitiven durch einen Extraktionsalgorithmus des Grauer-Schwerpunkt-Verfahrens positioniert wird, mit einem Berechnungsausdruck wie folgt:

wobei (i,j) den Pixelpunkt in einer Bildebene darstellt; es sich bei m und n um die Anzahl von Pixeln handelt, die in dem Bild in der Querrichtung und der Längsrichtung enthalten sind; (x,y) eine Masseschwerpunkt-Koordinate des Bilds ist; f(i,j) ein Grauwert an der Pixelkoordinate (i,j) ist;

fünfter Schritt: sechsdimensionale Berechnung für einen Konturfehler mit hoher Dynamik und großem Bereich einer CNC-Werkzeugmaschine, wobei

ein kleines Sichtfeld (21) in dem Verfahren verwendet wird, um die Messgenauigkeit der codierten Primitiven (8) im Sichtfeld zu verbessern; in Kombination mit Priori-Wissen der Monokularsicht-Pose-Algorithmus verwendet wird, um sichtmessbare Dimensions- und Interpolationsbereichskonturfehler von Maschinen zu begünstigen; die gesamte Werkzeugmaschinenbewegungskontur durch eine ausgewählte Referenzprimitive dargestellt wird; die Position der Referenzprimitive in einer unsichtbaren Region des Sichtfelds (21) durch die Pixelkoordinaten der Primitiven in einer sichtbaren Region in Kombination mit Priori-Einschränkungen mit hoher Genauigkeit berechnet wird; die Bewegungskontur, die durch die Referenzprimitive in dem Werkzeugmaschinenkoordinatensystem dargestellt ist, durch Datumstransformation durch Durchlaufen aller Bilder erhalten wird; ein sechsdimensionaler Konturfehler, der durch die Interpolation der CNC-Werkzeugmaschine (4) erzeugt wird, durch Vergleichen der gemessenen Kontur mit der Nennkontur berechnet wird; wobei sechsdimensionale Berechnungsschritte für einen Konturfehler mit hoher Dynamik und großem Bereich einer CNC-Werkzeugmaschine spezifisch wie folgt sind:

das Sichtfeld (21) der Kamera (1) NxN in mm-Einheiten ist; die externe Dimension der Priori-Standardplatte (7) MxM in mm-Einheiten ist; N viel kleiner als M ist; beteiligte Koordinatensysteme neben dem obigen globalen Koordinatensystem OG-XGYGZG (14) der Priori-Standardplatte außerdem ein Kamerakoordinatensystem OC-XCYCZC (13), ein Werkzeugmaschinenkoordinatensystem OM-XMYMZM (15) und ein lokales Koordinatensystem OLi-XLiYLiZLi (22) der Priori-Standardplatte umfassen; der Ausgangspunkt des Kamerakoordinatensystems OC-XCYCZC (13) auf einer optischen Mitte Oc ermittelt wird; wenn die CNC-Werkzeugmaschine sich nicht bewegt, vier codierte Primitive P11 16, P12 17, P13 18 und P14 19, die in einem Rechteck im Sichtfeld eingerichtet sind, im ersten Rahmenbild ausgewählt werden; die codierte Primitive P11 16 als eine Referenzprimitive ausgewählt wird; die Bewegungskontur der CNC-Werkzeugmaschine (4), die durch die Interpolationsbewegungsachse jeder Achse synthetisiert wird, durch die codierte Primitive P1116 dargestellt wird; die Koordinate im globalen Koordinatensystem OG-XGYGZG (14) der Priori-Standardplatte

ist; das Werkzeugmaschinenkoordinatensystem OM-XMYMZM (15) durch Nehmen von P11 16 als einem Ausgangspunkt ermittelt wird; die Richtung jeder Koordinatenachse des Werkzeugmaschinenkoordinatensystems OM-XMYMZM (15) mit der Richtung jeder Bewegungsachse der CNC-Werkzeugmaschine (4) übereinstimmt; die Werkzeugmaschine gesteuert wird, um die Messvorrichtung dazu anzutreiben, sich jeweils entlang der X-Richtung der Werkzeugmaschine in mehrere Positionen zu bewegen; die dreidimensionale Koordinate (x,y,z) von P1116 in Bezug auf das Kamerakoordinatensystem OC-XCYCZC (13) in jeder Position unter Verwendung eines Monokularsicht-Pose-Lösungsalgorithmus berechnet wird; auf dieser Basis ein Vektor in der X-Achsenrichtung angepasst wird; die Y-Achse des Werkzeugmaschinenkoordinatensystems OM-XMYMZM (15) gemäß derselben Regel bestimmt wird; die Z-Achse des Werkzeugmaschinenkoordinatensystems OM-XMYMZM (15) durch die Drei-Finger-Regel bestimmt wird; die X-Achse und die Y-Achse gemäß der folgenden Formel ermittelt werden:

wobei es sich bei

um die dreidimensionalen Koordinaten der codierten Primitive P11 16 im Kamerakoordinatensystem OcXcYcZc (13) im ersten Rahmenbild handelt; es sich bei (x', y', z') um die dreidimensionalen Koordinaten von Punkt P1116 in Bezug auf das Kamerakoordinatensystem OcXcYcZc (13) in jeder Position ist, die unter Verwendung des Monokularsicht-Pose-Lösungsalgorithmus durch die Messvorrichtung berechnet wurde, die sich entlang der X-Achsenrichtung der Werkzeugmaschine in mehrere Positionen bewegt; (mx, nx, px) ein Vektor in der X-Achsenrichtung des Werkzeugmaschinenkoordinatensystems OMXMYMZM (15) ist; es sich bei (CX, CY, CZ) um dreidimensionale Koordinaten eines Punkts im Kamerakoordinatensystem OcXcYcZc (13) handelt; es sich bei (MX, MY, MZ) um dreidimensionale Koordinaten eines Punkts im Werkzeugmaschinenkoordinatensystem OMXMYMZM (15) handelt;

eine Transformationsmatrix zwischen dem Kamerakoordinatensystem OcXcYcZc (13) und dem Werkzeugmaschinenkoordinatensystem OMXMYMZM (15) ist;

die Priori-Standardplatte (7) während einer Messung kontinuierlich eine Interpolationsbewegung zusammen mit der Werkzeugmaschine vornimmt und die codierten Primitive (8) darauf kontinuierlich auf der Kamera (1) abgebildet werden; die Kamera (1) im Bewegungsvorgang der CNC-Werkzeugmaschine (4) insgesamt G Rahmenbilder sammelt; vier codierte Primitive (8), die in dem Sichtfeld in dem i-ten Rahmenbild auftreten und in einem Rechteck eingerichtet sind, P11 23, P12 24, P13 25 und P14 26 sind; die Koordinaten der Mitten der vier codierten Primitive (8) im globalen Koordinatensystem OGXGYGZG (14) der Priori-Standardplatte





und

sind; entsprechende zweidimensionale Pixelkoordinaten auf der Bildebene





und

sind; ein lokales Koordinatensystem OLiXLiYLiZLi (22) der Priori-Standardplatte unter dem i-ten Rahmen ermittelt wird, wobei i eine ganze Zahl zwischen 1 und G ist; das Koordinatensystem P11 23 als einen Koordinatenausgangspunkt nimmt; XLi- und YLi-Koordinatenachsenrichtungen parallel zu einer XG- bzw. YG-Richtung des globalen Koordinatensystems OGXGYGZG (14) der Priori-Standardplatte sind; eine ZLi-Koordinatenachse durch die Drei-Finger-Regel bestimmt wird; dreidimensionale Koordinaten der Mitten der ausgewählten vier codierten Primitive (8) im lokalen Koordinatensystem OLiXLiYLiZLi (22) der Priori-Standardplatte sind:

wobei m = 1, 2, 3, 4 und Ti eine Transformationsmatrix zwischen dem globalen Koordinatensystem OGXGYGZG (14) der Priori-Standardplatte des i-ten Rahmenbilds und dem lokalen Koordinatensystem OLiXLiYLiZLi (22) der Priori-Standardplatte ist; das i-te Rahmenbild gemäß der folgenden Gleichung A berechnet wird:

wobei Xi ein Abstand von der optischen Mitte Oc im Kamerakoordinatensystem OCXCYCZC (13) zum P11 -23-Punkt auf der Priori-Standardplatte (7) des i-ten Rahmens ist; Yi ein Abstand von der optischen Mitte Oc im Kamerakoordinatensystem OCXCYCZC (13) zum P12 -24-Punkt auf der Priori-Standardplatte (7) des i-ten Rahmens ist; Zi ein Abstand von der optischen Mitte Oc im Kamerakoordinatensystem OCXCYCZC (13) zum P14 -26-Punkt auf der Priori-Standardplatte (7) des i-ten Rahmens ist; a' ein Abstand zwischen P11 23 und P12 24 im globalen Koordinatensystem OGXGYGZG (14) der Priori-Standardplatte (7) des i-ten Rahmens ist; b' ein Abstand zwischen P12 24 und P14 26 im globalen Koordinatensystem OGXGYGZG (14) der Priori-Standardplatte (7) des i-ten Rahmens ist; c' ein Abstand zwischen P11 23 und P14 26 im globalen Koordinatensystem OGXGYGZG (14) der Priori-Standardplatte (7) des i-ten Rahmens ist; α ein Winkel ∠Pi2OCPi4 zwischen geraden Linien OCP12 und OCP14 ist; β ein Winkel ∠Pi1OCPi4 zwischen geraden Linien OCP11 und OCP14 ist; γ ein Winkel ∠Pi21OCPi2 zwischen geraden Linien OCP11 und OCP12 ist;





k = 2cosα, q = 2cosβ, r = 2cosγ, c'2 = VZi2 a'2 = ac'2 = avZi2, b'2 = bc'2 = bvZi2, Xi = xZi, Yi = yzi, P11 23, P12 24 und P14 26 als drei Raumpunkte im i-ten Rahmen eingestellt sind, die nicht koplanar sind und deren Positionsbeziehung bekannt ist, und k2 + q2 + r2 - kqr - 1 ≠ 0 erfüllt ist; Gleichung A als Formel B umgeschrieben ist:

die ausgeartete Lösung von Formel B durch einen Optimierungsalgorithmus eliminiert wird, um vier akzeptable Null-Lösungen zu erhalten; P13 25 als eine Priori-Einschränkung verwendet wird, um einzigartige Lösungen von Xi, Yi und Zi zu erhalten; dann dreidimensionale Koordinaten



und

von P11 -23-, P12 -24- und P14 -26-Punkten auf der Priori-Standardplatte (7) des i-ten Rahmens unter dem Kamerakoordinatensystem OcXcYcZc (13) als die folgende Formel ausgedrückt werden:

wobei j = 1, 2, 4 und i = 1, 2 ... G; auf der Basis der bekannten LiPji(LiXji, LiYji, LiZji) und cPji (cXji, cYji, cZji) ein Kabsch-Algorithmus zum Lösen einer Rotationsmatrix R'i und einer Translationsmatrix t'i des lokalen Koordinatensystems OLiXLiYLiZLi (22) der Priori-Standardplatte des i-ten Rahmens in Bezug auf das Kamerakoordinatensystem OcXcYcZc (13) verwendet wird; es sich bei t'i um die dreidimensionalen Koordinaten t'i = cPji (cXji, cYji, cZji) des Ausgangspunkts P11 23 des lokalen Koordinatensystems OLiXLiYLiZLi (22) der Priori-Standardplatte des i-ten Rahmens im Kamerakoordinatensystem OcXcYcZc (13) handelt; ein Nickwinkel θ'i, ein Rollwinkel Φ'i und ein Gierwinkel Ψ'i zwischen zwei Koordinatensystemen durch R'i-Trennung berechnet werden; die dreidimensionalen Koordinaten (cXi, cYi, cZi), mit

der Referenzprimitive P11 im Kamerakoordinatensystem OCXCYCZC (13) des i-ten Rahmens gemäß einer bekannten Raumeinschränkung unter den codierten Primitiven (8) der Priori-Standardplatte (7) berechnet wird;

der gemessene Konturfehler im Werkzeugmaschinenkoordinatensystem OMXMYMZM und die von der Kamera (1) gemessene Kontur einer Koordinatentransformation unterzogen werden muss, um den Werkzeugmaschinenkonturfehler korrekt zu berechnen; eine Pose-Transformationsformel des Werkzeugmaschinenkoordinatensystems OMXMYMZM (15) und des lokalen Koordinatensystems OLiXLiYLiZLi (22) der Priori-Standardplatte ist:

wobei M eine Transformationsmatrix zwischen dem lokalen Koordinationssystem OLiXLiYLiZLi (22) der Priori-Standardplatte unter dem i-ten Rahmenbild und dem Werkzeugmaschinenkoordinatensystem OMXMYMZM (15) ist; ein Nickwinkel θi, ein Rollwinkel Φi und ein Gierwinkel Ψi der i-ten Rahmen-Standardplatte in Bezug auf das Werkzeugmaschinenkoordinatensystem OMXMYMZM (15) von Mi getrennt werden; alle Bildsequenzen durchlaufen werden, um eine Sechs-Freiheitsgrade-Kontur Lr der gesamten Werkzeugmaschine zu erhalten, die durch die Referenzprimitive dargestellt wird, wobei Lr (MXi, MYi, MZi, θi, Φi, Ψi) und i = 1, 2 ... G; ein Sechs-Freiheitsgrade-Konturfehler E, der durch eine Interpolation der CNC-Werkzeugmaschine (4) erzeugt wird, durch Vergleichen der tatsächlichen Sechs-Freiheitsgrade-Kontur Lr mit der Nennkontur Lm berechnet wird: E = Lr - Lm.


 


Revendications

1. Procédé de mesure en six dimensions en vision monoculaire pour une erreur de contour arbitraire à large plage hautement dynamique d'une machine-outil CNC, dans lequel le procédé utilise un dispositif de mesure et un système de mesure qui sont spécialement conçus, et en combinaison avec une connaissance préalable, l'algorithme de pose de vision monoculaire est utilisé pour promouvoir la dimension mesurable de la vision et la plage des erreurs de contour d'interpolation de machines ; l'ensemble du contour de mouvement de la machine-outil est représenté par une primitive de référence sélectionnée ; un petit champ de vision est utilisé pour améliorer la précision de mesure des primitives visibles codées ; puis, des informations en six dimensions de X, Y, Z, tangage, roulis et lacet du contour d'interpolation de machine-outil représenté par la primitive de référence dans le système de coordonnées de machine-outil sont obtenues par transformation de référence ; le procédé est utilisé pour parcourir chaque image de trame de prise de vue afin d'obtenir le contour de mouvement en six dimensions réel final de la machine-outil ; une erreur de contour en six dimensions générée par l'interpolation d'une machine-outil CNC est calculée en comparant le contour mesuré avec le contour nominal ; dans lequel le procédé comprend les étapes suivantes :

première étape : installer le dispositif de mesure et le système de mesure spécialement conçus, dans lequel le dispositif de mesure spécialement conçu est composé d'une base (10), d'une unité électroluminescente de courte durée à haute luminosité (9), d'une plaque standard a priori (7) et de primitives codées (8) ; la plaque standard a priori (7) est constituée d'un matériau de base transparent, et les primitives codées (8) avec des valeurs de code uniques et une distribution de matrice sont enduites sur la plaque standard a priori (7) ; lorsque le dispositif de mesure est installé, l'unité électroluminescente de courte durée à haute luminosité (9) est insérée dans des rainures sur les deux côtés de la base (10) ; la plaque standard (7) a priori est supportée sur la base (10) ; la plaque standard (7) a priori est pressée par deux plaques de pression (6) ; quatre boulons de verrouillage de plaque de pression (5) sont utilisés pour presser et fixer la plaque standard a priori (7) à travers les plaques de pression (6) ;
le système de mesure comprend une caméra (1), une pince pour caméra (2) et le dispositif de mesure ; la caméra (1) est fixée à la pince de caméra (2); la pince de caméra (2) est installée au-dessus du dispositif de mesure pour collecter des images séquentielles dans le processus de mouvement du dispositif de mesure ; le dispositif de mesure assemblé est placé sur une plate-forme de dispositif optique à trois coordonnées ; un dispositif optique à trois coordonnées étalonne une relation de géométrie spatiale parmi les primitives codées (8) sous un système de coordonnées global de la plaque standard a priori ; lorsque le système de mesure est disposé, le dispositif de mesure étalonné est fixé à une table rotative (3) de la machine-outil CNC (4) au moyen d'un boulon de pression (11) et d'un écrou de pression (12) ;

deuxième étape : établir le système de coordonnées global de la plaque standard a priori, dans lequel le système de coordonnées global OGXGYGZG (14) de la plaque standard a priori est établi sur le dispositif de mesure ; une origine est établie au centre de la primitive codée (8) dans la première ligne et la première colonne, et est définie comme OG ; la direction de l'axe des coordonnées XG est que l'origine OG vers le bas pointe vers le point central de la primitive codée (8) dans la première colonne et la dernière ligne du tableau ; la direction de l'axe des coordonnées YG est que OG pointe vers la droite vers le point central de la primitive codée (8) dans la première ligne et la dernière colonne du tableau ; l'axe des coordonnées ZG est déterminé par une règle de droite ; le dispositif optique à trois coordonnées est utilisé pour étalonner la relation de géométrie spatiale parmi les primitives codées (8) sous le système de coordonnées global OGXGYGZG (14) de la plaque standard a priori pour obtenir les coordonnées tridimensionnelles des primitives codées (8) sous le système de coordonnées global OGXGYGZG (14) de la plaque standard a priori ; les primitives codées (8) sur la plaque standard a priori (7) portent des informations de mouvement de la machine-outil CNC (4) ; la relation de position spatiale entre les primitives codées (8) est étalonnée par un dispositif de haute précision ; en supposant que la précision de l'étalonnage est assurée, la taille de la plaque standard a priori (7) peut être rendue aussi grande que possible pour satisfaire les exigences de mesure à grande échelle de l'erreur de contour ;

troisième étape : étalonnage de la caméra, dans lequel un modèle d'imagerie de caméra exprime une relation de cartographie biunivoque entre un système de coordonnées de caméra et un système de coordonnées global ; le modèle d'imagerie de caméra comportant des paramètres de distorsion est :

(Xw,Yw,Zw) sont des coordonnées tridimensionnelles du point central de la primitive codée (8) sous le système de coordonnées global ; K est une matrice intrinsèque de la caméra (1) ; T est une matrice extrinsèque de la caméra (1) ; (u, v) sont des coordonnées bidimensionnelles du point central de la primitive codée (8) dans un plan d'image; (u0,v0) sont les coordonnées du point principal ; (Cx,Cy) est une distance focale équivalente dans les directions transversale et longitudinale;

et

sont respectivement des matrices de transformation de rotation et de translation entre le système de coordonnées de caméra et le système de coordonnées global ; x, δy) est une distorsion d'un point d'image dans les directions de x et y causées par un système optique imparfait ; un panneau d'étalonnage de vérificateur est placé dans plusieurs positions dans le champ de vision (21) de la caméra (1) et les images sont acquises; les paramètres de distorsion ainsi que les matrices intrinsèques et extrinsèques de la caméra (1) sont étalonnés par un algorithme d'étalonnage ;

quatrième étape : collecte et traitement d'images haute définition sans flou pour le contour d'interpolation à large plage hautement dynamique de machine-outil CNC dans lequel,
sur la base de l'installation et de l'agencement du dispositif de mesure, des images du contour interpolé par la machine-outil CNC (4) sont collectées ; parce que les exigences pour la précision de mesure de l'erreur de contour sont élevées, le champ de vision requis (21) pour la prise de vue est petit ; tout d'abord, les paramètres de la caméra (1) sont ajustés de sorte que la caméra (1) se trouve sous le champ de vision et à la fréquence de prise de vue optimaux ; ensuite, la caméra (1) et l'unité électroluminescente de courte durée à haute luminosité (9) sont déclenchées de manière synchrone ; le temps d'émission de lumière et l'intensité d'émission de lumière de l'unité électroluminescente de courte durée à haute luminosité (9) sont réglés de manière à garantir que l'unité électroluminescente de courte durée à haute luminosité (9) pénètre à travers la base de la plaque standard a priori (7) pendant le temps d'exposition de la caméra (1) et complète la lumière pour les primitives codées (8) ; une vitesse de machine-outil à vitesse de déplacement élevée qui peut refléter les performances dynamiques de la machine-outil est sélectionnée ; chaque axe de mouvement de la machine-outil CNC (4) est entraîné pour interpoler le contour conformément aux instructions du programme ; dans le processus de collecte d'images du mouvement de la machine-outil, la caméra (1) est fixe et la machine-outil se déplace ; des images séquentielles claires et non floues des primitives codées (8) sont collectées avec l'aide de l'unité électroluminescente de courte durée à haute luminosité (9) ; une fois les images collectées, les valeurs de code représentées par chaque primitive codée (8) sur les images sont reconnues, puis les coordonnées en pixels bidimensionnelles du point central de chaque primitive codée décodée (8) sont positionnées par une méthode du centroïde gris ; le centre des primitives codées est positionné par un algorithme d'extraction de la méthode du centroïde gris, avec une expression de calcul comme suit :

(i,j) représente le point de pixel dans le plan d'image ; m et n sont le nombre de pixels inclus dans l'image dans la direction transversale et la direction longitudinale ; (x, y) sont des coordonnées du centre de masse de l'image ; f(i,j) est une valeur de gris aux coordonnées de pixel (i,j) ;

cinquième étape : calcul en six dimensions pour l'erreur de contour arbitraire à large plage hautement dynamique de la machine-outil CNC dans lequel,
dans le procédé, un petit champ de vision (21) est utilisé pour améliorer la précision de mesure des primitives codées (8) dans le champ de vision ; en combinaison avec la connaissance préalable, l'algorithme de pose de vision monoculaire est utilisé pour promouvoir la dimension mesurable de la vision et la plage des erreurs de contour d'interpolation des machines ; l'ensemble du contour de mouvement de la machine-outil est représenté par une primitive de référence sélectionnée ; la position de la primitive de référence dans une région invisible du champ de vision (21) est calculée par les coordonnées de pixel des primitives dans la région visible en combinaison avec des contraintes a priori de haute précision ; le contour de mouvement représenté par la primitive de référence dans le système de coordonnées de la machine-outil est obtenu par transformation de référence en parcourant toutes les images ; une erreur de contour en six dimensions générée par l'interpolation de la machine-outil CNC (4) est calculée en comparant le contour mesuré avec le contour nominal ;
dans lequel
les étapes de calcul en six dimensions pour l'erreur de contour arbitraire à large plage hautement dynamique de la machine-outil CNC sont spécifiquement les suivantes :

le champ de vision (21) de la caméra (1) est

NxN en unités de mm ; les dimensions externes de la plaque standard a priori (7) est MxM en unités de mm ; N est bien inférieur à M ; outre le système de coordonnées global OG-XGYGZG (14) ci-dessus de la plaque standard a priori, les systèmes de coordonnées impliqués comprennent également un système de coordonnées de caméra Oc-XcYcZc (13), un système de coordonnées de machine-outil OM-XMYMZM (15) et un système de coordonnées local OLiXLiYLiZLi (22) de la plaque standard a priori ; l'origine du système de coordonnées de caméra Oc-XCYcZc (13) est établie sur un centre optique Oc ; lorsque la machine-outil CNC (4) ne bouge





pas,

quatre primitives codées et disposées selon un rectangle dans le champ de vision sont sélectionnées dans la première image

de trame ; la primitive codée est sélectionnée comme primitive de référence ; le contour de mouvement de la machine-outil CNC (4) synthétisé par l'axe de mouvement d'interpolation de

chaque axe est représenté par la primitive codée ; les coordonnée dans le système de coordonnées global OG-

XGyGZG (14) de la plaque standard a priori sont ; le système de coordonnées de machine-outil OM-XMYMZM (15) est établi en prenant comme origine ; la direction de chaque axe de coordonnées du système de coordonnées de machine-outil OM-XMYMZM (15) est cohérente avec la direction de chaque axe de mouvement de la machine-outil CNC (4); la machine-outil est commandée pour entraîner le dispositif de mesure pour se déplacer respectivement le long de la direction de l'axe X de la machine-outil vers plusieurs positions ; les coordonnées tridimensionnelles (x, y, z) de par rapport au système de coordonnées de caméra Oc-XcYcZc (13) dans chaque position sont calculées en utilisant un algorithme de résolution de pose de vision monoculaire ; sur cette base, un vecteur dans la direction de l'axe X est ajusté ; l'axe Y du

système de coordonnées de machine-outil OM-XMYMZM (15) est déterminé conformément à la même règle ; l'axe Z du système de coordonnées de machine-outil OM-XMYMZM (15) est déterminé par la règle de droite ; l'axe X et l'axe Y sont établis selon la formule suivante:



sont les coordonnées tridimensionnelles de la primitive codée

dans le système de coordonnées de caméra OcXcYcZc (13) dans la première image de trame ; (x',y',z) sont les coordonnées tridimensionnelles du point

par rapport au système de coordonnées de caméra OcXcYcZc (13) dans chaque position calculée en utilisant l'algorithme de résolution de pose de vision monoculaire par le dispositif de mesure qui se déplace le long de la direction de l'axe X de la machine-outil vers plusieurs positions ; (mx,nx,Px} est un vecteur dans la direction de l'axe X du système de coordonnées de machine-outil OMXMYMZM (15) ; (my,ny,py) est un vecteur dans la direction de l'axe Y du système de coordonnée de machine-outil OMXMYMZM (15) ; (cX, cY, cZ) sont des coordonnées tridimensionnelles d'un point dans le système de coordonnées de caméra OcXcYcZc (13); (MX , MY, MZ) sont des coordonnées tridimensionnelles d'un point dans le système de coordonnées de machine-outil OMXMYMZM (15) ;

est une matrice de transformation entre le système de coordonnées de caméra OcXcYcZc (13) et le système de coordonnées de machine-outil OMXMYMZM (15) ;





pendant la mesure, la plaque standard a priori (7) effectue en continu un mouvement







d'interpolation avec la machine-outil, et les primitives codées (8) sur celle-ci sont imagées en continu sur la caméra (1) ; dans le processus de mouvement de la









machine-outil CNC (4), la caméra (1) collecte totalement G images de trame; quatre primitives codées (8) qui apparaissent dans



le champ de vision dans la ième image de trame et disposées selon un rectangle sont et ;les coordonnées des centres des quatre primitives codées (8) dans le système de coordonnées global OGXGYGZG (14) de la plaque standard a priori sont et les coordonnées de pixels bidimensionnelles correspondantes sur le plan de l'image sont et un système de coordonnées locale OLiXLiYLiZLi (22) de la plaque standard a priori sous la ième trame est établi, où i est un nombre entier compris entre 1 et G ; le système de coordonnées prend comme origine de coordonnées ; les directions des axes de coordonnées XLI et YLI sont respectivement parallèles aux directions XG et YG du système de coordonnées global OGXGYGZG (14) de la plaque standard a priori ; l'axe des coordonnées ZU est déterminé par la règle de droite ; les coordonnées tridimensionnelles des centres des quatre primitives codées sélectionnées (8) dans le système de coordonnées local OLiXLiYLiZLi (22) de la plaque standard a priori sont :

où m=1,2,3,4 et Ti est une matrice de transformation entre le système de coordonnées global OGXGYGZG(14) de la plaque standard a priori de la ième image de trame et le système de coordonnées local OLiXLiYLiZLi (22) de la plaque standard a priori ; la ième image de trame est

calculée selon l'équation A suivante :

Xi est une distance entre le centre optique Oc dans le système de coordonnées de caméra OcXcYcZc (13) et le point

23 sur la plaque standard a priori (7) de la ième trame ;

Yi est une distance entre le centre optique Oc dans le système de coordonnées de caméra OcXcYcZc (13) et le point

sur la plaque standard a priori (7) de la ième trame ; Zi est une distance entre le centre optique Oc dans le système de coordonnées de caméra OcXcYcZc (13) et le point

sur la plaque standard a priori (7) de la ième trame ; a' est une distance entre

et

dans le système de coordonnées global OGXGYGZG de la plaque standard a priori (7) de la ième trame ; b' est une distance entre

et

dans le système de coordonnées global OGXGYGZG (14) de la plaque standard a priori de la ième trame ; c' est une distance entre

et

dans le système de coordonnées global OGXGYGZG(14) de la plaque standard a priori de la ième trame ; α est un angle

entre les droites

et

β est un angle

entre les droites

et

γ est un angle

entre les droites

et







k=2cosα, q=2cosβ, r=2cosy, c'2=yZi2, a'2=ac'2=avZi2, b2=bc'2=bvZi2, Xi=xZi Yi=yZi



et

sont définis comme trois points spatiaux dans la ième trame qui ne sont pas coplanaires et dont la relation de position est connue, et k2 +q2+r2-kqr-1≠0 est satisfaite ; l'équation A est réécrite sous forme de la formule B :

la solution dégénérée de la formule B est éliminée par un algorithme d'optimisation pour obtenir quatre solutions zéro acceptables ;

est utilisé comme contrainte a priori pour obtenir des solutions uniques de Xi, Yi et Zi ; puis des coordonnées tridimensionnelles



et

des points



et

sur la plaque standard a priori (7) de la ième trame sous le système de coordonnées de caméra OcXcYcZc (13) sont exprimées par la formule suivante :

où j = 1,2,4 et i = 1,2...G ; sur la base des

et

connus, un algorithme de Kabsch est utilisé pour résoudre une matrice de rotation R'i et une matrice de translation t'i du système de coordonnées local OLiXLiYLiZLi (22) de la plaque standard a priori de la ième trame par rapport au système de coordonnées de caméra Oc-XcYcZc (13) ; t'i est les coordonnées tridimensionnelles

de l'origine

du système de coordonnées local OLiXLiYLiZLi (22) de la plaque standard a priori de la ième trame dans le système de coordonnées de caméra OcXcYcZc (13) ; un angle de tangage

un angle de roulis

et un angle de lacet

entre deux systèmes de coordonnées sont calculés au moyen de de la séparation R'¡ ; les coordonnées tridimensionnelles (CXi, CYi, CZi) avec

de la primitive de référence

dans le système de coordonnées de caméra, OcXcYcZc (13) de la ième trame est calculé selon une contrainte spatiale connue parmi les primitives codées (8) de la plaque standard a priori (7) ;

l'erreur de contour mesurée est représentée dans le système de coordonnées de machine-outil OMXMYMZM (15) et le contour mesuré par la caméra (1) doit être soumis à une transformation de coordonnées pour calculer correctement l'erreur de contour de la machine-outil ; une formule de transformation de pose du système de coordonnées de machine-outil OMXMYMZM (15) et du système de coordonnées local OLiXLiYLiZLi (22) de la plaque standard a priori est :

Mi est une matrice de transformation entre le système de coordonnées local OLiXLiYLiZLi (22) de la plaque standard a priori sous la ième image de trame et le système de coordonnées de machine-outil OMXMYMZM (15); un angle de tangage θi, un angle de roulis Φi et un angle de lacet ψi de la ième plaque standard de trame par rapport au système de coordonnées de machine-outil OMXMYMZM (15) sont séparés de Mi ; toutes les séquences d'images sont parcourues pour obtenir un contour Lr à six degrés de liberté de l'ensemble de la machine-outil représenté par la primitive de référence, où Lr(MXi, MYi, MZi, θi, Φi, ψi) et i = 1,2...G ; une erreur de contour E à six degrés de liberté générée par l'interpolation de la machine-outil CNC (4) est calculée en comparant le contour réel à six degrés de liberté Lr avec le contour nominal Lm :


 




Drawing




















Cited references

REFERENCES CITED IN THE DESCRIPTION



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Patent documents cited in the description




Non-patent literature cited in the description